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From:   Kees Cook <keescook@chromium.org>
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     Kees Cook <keescook@chromium.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        Eric Biggers <ebiggers3@gmail.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        linux-fsdevel@vger.kernel.org,
        linux-security-module@vger.kernel.org, linux-api@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH 4/4] fs: Include FMODE_EXEC when converting flags to f_mode
Date:   Sun, 17 May 2020 22:54:57 -0700
Message-Id: <20200518055457.12302-5-keescook@chromium.org>
In-Reply-To: <20200518055457.12302-1-keescook@chromium.org>
References: <20200518055457.12302-1-keescook@chromium.org>
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Sender: linux-kernel-owner@vger.kernel.org
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Include FMODE_EXEC when building the f_mode field, so that code can
actually test the correct field and values. Only three places actually
examine f_flags for FMODE_EXEC:

fs/open.c:      if (unlikely((f->f_mode & FMODE_EXEC) && !S_ISREG(inode->i_mode))) {
include/linux/fsnotify.h:               if (file->f_mode & FMODE_EXEC) {
include/linux/fsnotify.h:       if (file->f_mode & FMODE_EXEC)

Signed-off-by: Kees Cook <keescook@chromium.org>
---
I assume there must be some reason for FMODE_EXEC not being pulled into
f_mode, but I couldn't find it. I guess this is my attempt to either fix
an oversight or to learn by flames. :)
---
 fs/namei.c               | 4 ++--
 include/linux/fs.h       | 3 ++-
 include/linux/fsnotify.h | 4 ++--
 3 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 6bb1b6624bad..362b1cc75f5c 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3213,8 +3213,8 @@ static int do_open(struct nameidata *nd,
 		return -ENOTDIR;
 
 	/* Opening for execution requires a regular file on an exec mnt. */
-	if ((file->f_flags & FMODE_EXEC) && (!d_is_reg(nd->path.dentry) ||
-					     path_noexec(&nd->path)))
+	if ((file->f_mode & FMODE_EXEC) && (!d_is_reg(nd->path.dentry) ||
+					    path_noexec(&nd->path)))
 		return -EACCES;
 
 	do_truncate = false;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 4f6f59b4f22a..8a2cabdcf531 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3545,10 +3545,11 @@ int __init get_filesystem_list(char *buf);
 
 #define __FMODE_EXEC		((__force int) FMODE_EXEC)
 #define __FMODE_NONOTIFY	((__force int) FMODE_NONOTIFY)
+#define __SMUGGLED_FMODE_FLAGS	(__FMODE_EXEC | __FMODE_NONOTIFY)
 
 #define ACC_MODE(x) ("\004\002\006\006"[(x)&O_ACCMODE])
 #define OPEN_FMODE(flag) ((__force fmode_t)(((flag + 1) & O_ACCMODE) | \
-					    (flag & __FMODE_NONOTIFY)))
+					    (flag & __SMUGGLED_FMODE_FLAGS)))
 
 static inline bool is_sxid(umode_t mode)
 {
diff --git a/include/linux/fsnotify.h b/include/linux/fsnotify.h
index 5ab28f6c7d26..86761ed4b434 100644
--- a/include/linux/fsnotify.h
+++ b/include/linux/fsnotify.h
@@ -90,7 +90,7 @@ static inline int fsnotify_perm(struct file *file, int mask)
 	if (mask & MAY_OPEN) {
 		fsnotify_mask = FS_OPEN_PERM;
 
-		if (file->f_flags & __FMODE_EXEC) {
+		if (file->f_mode & FMODE_EXEC) {
 			ret = fsnotify_file(file, FS_OPEN_EXEC_PERM);
 
 			if (ret)
@@ -264,7 +264,7 @@ static inline void fsnotify_open(struct file *file)
 {
 	__u32 mask = FS_OPEN;
 
-	if (file->f_flags & __FMODE_EXEC)
+	if (file->f_mode & FMODE_EXEC)
 		mask |= FS_OPEN_EXEC;
 
 	fsnotify_file(file, mask);
-- 
2.20.1